A dosimeter of this kind is disclosed in U.S. Pat. No. 3,620,677. This dosimeter includes a housing which closely encloses a strip-like wick and is in contact engagement therewith. The wick can take on different geometric forms. The specimen to be investigated diffuses along the wick and brings about a coloration as a consequence of a chemical reaction with an indicator substance provided on the wick. Either more or less quantities of an indicator substance are provided in dependence upon the contour of the strip-like duct whereby the detection sensitivity for larger or smaller quantities of contaminants is determined.
Since the strip-like indicator strip of the known dosimeter completely fills out the indicator housing, a diffusion of gaseous material to be detected is greatly restricted and requires a correspondingly long diffusion time. In particular, these diffusion times become impermissibly long if the smallest quantities of gaseous contaminants are to be detected.